BOOK V. 
GEOGRAPHY. 
495 
most sensibly those families that abound in alpine species ; as, 
for instance, Gramineae and Compositse. At 6000 feet of 
elevation, the mean temperature of the air, on the back of the 
equatorial Andes, is 62° 6', which is equal to that of July at 
Paris. Although, upon the table-land of the Cordilleras, we 
find the same annual temperature as in high latitudes, yet it 
is not right to generalise too much such analogies between 
the temperate climates of equatorial mountains and low sta- 
tions in the circumpolar zone. These analogies are not so 
great as is supposed ; they are much influenced by the partial 
distribution of heat in different seasons of the year. The 
quotient does not regularly change, in rising from the plains 
into the mountains, in the same manner as it does in ap- 
proaching the pole; as happens with Monocotyledones in 
general, ferns, and Compositae. 
" We may, moreover, remark, that the developement of the 
vegetation of different families depends neither upon geogra- 
phical or isothermal latitude alone ; but that, on the con- 
trary, the quotients are not in accordance on the same 
isothermal line of the temperate zone in the plains of America 
and of the old world. Under the tropics, there is a remark- 
able difference between America, India, and the western side 
of Africa. The distribution of organised beings over the 
surface of the globe depends not only upon very complicated 
conditions of climate, but also upon geological causes, the 
nature of which is wholly unknown, but which are connected 
with the original state of our planet. In the equinoctial zone 
of Africa palms are not very numerous, if compared with the 
much greater number in South America. Differences such 
as these, far from turning us from a search after the laws 
of nature, should, on the contrary, excite us to contemplate 
those laws in their most complicated forms. Lines of equal 
heat do not follow the parallel of the equator ; they have con- 
vex and concave summits, which are distributed very regularly 
over the globe, and form different systems along the eastern 
and western sides of the two worlds, in the centre of conti- 
nents, and in the vicinity of oceans. It is probable that, 
when the globe shall have been more correctly examined, it 
will be found that the lines of maxima of grouping (that is, 
